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P0305 Fault Code Diagnosis - 2008 Jeep Liberty 3.7L V6 | Freeze Frame Data Analysis

Model: Jeep Liberty Fault Code: P0305 Posted: 2013-06-27 08:13

Good morning, I'm working on a persistent P0305 misfire issue in my 2008 Jeep Liberty with the 3.7L V6 engine. I've been troubleshooting this for over two weeks and have completed the following steps: - Replaced spark plugs - Swapped coil positions (cylinder 5 to other cylinders) - Swapped injector positions - Conducted a compression test showing 180 psi on cylinder 5 - Performed visual inspection of injector wiring — no signs of damage or loose connections The fault code does not follow the coil or injector repositioning, which suggests the issue is not in those components. Key observations from the freeze frame data: - Long-term fuel trim at +7% for Bank 2 (indicating a lean condition on cylinder 5) - Vehicle speed at MIL trigger: 1 MPH — extremely low - Engine RPM at MIL trigger: 150 RPM — unusually low for normal idle conditions - Throttle position and load values are inconsistent with these readings, suggesting potential sensor or data logging issues Given this behavior, I suspect a possible issue with the engine control module (ECM/PCM), though I'm open to other explanations. Has anyone else encountered similar P0305 symptoms in a 2008 Jeep Liberty? Any suggestions on next steps? Thanks, Mr502

Related fault codes

P0305

Comments (4)

Anonymous 2013-06-28 06:11

The MAP sensor shows low vacuum (10 PSI). This points to a possible vacuum leak near cylinder 5. Try spraying carb cleaner around the intake manifold gaskets and monitor idle RPM for any changes. A sudden increase in RPM could confirm a leak.

Anonymous 2013-06-28 07:10

Great suggestion, thanks Mohawk! I actually needed carb cleaner this weekend anyway — perfect timing. I'll test it out and report back. Does anyone have insight into the unusual RPM/speed readings at MIL trigger?

Anonymous 2013-06-30 16:22

It's highly unlikely to be a faulty PCM. In addition to your compression test, you should perform a cylinder leakage test — many 2008 Jeep Liberty engines have valve sealing issues that pass static compression tests but show significant leaks during operation. As for the low RPM and speed at MIL trigger: this may point to software interpretation errors in your OBD-II scanner. If your PCM can properly fire coils and injectors, it's likely functioning correctly — the data discrepancy might stem from tool calibration or sensor timing issues.

Anonymous 2013-06-30 20:08

Thanks for the clear explanation, Jeff! I tested this weekend with my daughter driving. The misfire only occurs at idle — no symptoms during cruise, acceleration, or deceleration. This suggests that cylinder pressure is sufficient under normal operating conditions but fails at low RPMs. I couldn't detect any vacuum leaks and don’t have access to a leak-down gauge right now. I’ll try borrowing one soon. My hypothesis: the engine has adequate compression at higher speeds, but significant internal leakage at idle — possibly due to worn valves or seals. Free software tools may help with deeper data analysis. Thanks for all the input!